The amount of organic substances contained in low-impurity water such as water for pharmaceutical production, process water for semiconductor manufacturing, cooling water, boiler water, or tap water is monitored by measuring the TOC content of a water sample.
Examples of a total organic carbon measuring method include a combustion oxidation method in which organic substances are oxidized by combustion in a high-temperature furnace and a wet oxidation method in which organic substances are chemically oxidized using UV light and oxidants. In the case of TOC measurements of pure water and ultra-pure water requiring high sensitivity, the latter, that is, a wet oxidation method is generally used.
As a method for measuring TOC by wet oxidation, there is a method including the steps of: converting organic substances contained in a water sample to carbon dioxide by an oxidation reactor; transferring the carbon dioxide into measurement water through a gas-permeable membrane; and feeding the measurement water containing the carbon dioxide transferred from the water sample to a conductivity measuring unit to measure the conductivity of the measurement water to detect the concentration of carbon dioxide (see Patent Documents 1 and 2).
Further, as conductivity measurement of carbon dioxide, there is also a method of measuring TOC of an organic compound in which at least two electrodes are provided at positions before and after oxidation, and a difference in the conductivity of the water sample between before and after oxidation is detected (see Patent Document 3).
As a method for measuring the TOC content of low-impurity water such as process water for semiconductor manufacturing or water for pharmaceutical production, there is a method in which organic substances contained in a water sample are decomposed by UV light to carbon dioxide, the carbon dioxide is transferred into measurement water through a carbon dioxide separation part, and the conductivity of the measurement water is measured. Such a method is known as a method capable of measuring the TOC content of low-impurity water with high accuracy using a relatively compact instrument.
The present inventors have already developed a total organic carbon measuring instrument obtained by integrating some devices using a microfabrication technique to suggest a reduction in the volume of water to be measured as compared to conventional measuring instruments (see Patent Document 4). This TOC measuring instrument is intended to achieve both a reduction in the consumption of a water sample and a reduction in the influence of elution of piping materials and/or the influence of carbon dioxide to be transferred.
Patent Document 1: Japanese Patent No. 2510368
Patent Document 2: Japanese Patent Application Laid-open No. 2006-90732
Patent Document 3: Japanese Patent Application Laid-open No. 2001-281189
Patent Document 4: Japanese Patent Application Laid-open No. 2006-300633